1. Field of the Disclosure
Embodiments of the present invention relate to an image sensor with an improved dynamic range.
2. Discussion of the Related Art
The image sensor is a semiconductor device for converting an optical image to an electric signal. In the image sensors, there are CCD (Charge Coupled Device) type devices and CMOS (Complementary Metal-Oxide-Silicon) type devices.
The CCD (Charge Coupled Device) has a complicated driving system, high power consumption, complicated fabrication process due to many masking steps, and difficulty in fabricating into one chip because a signal processing circuit cannot be integrated to the chip. In contrast, the CMOS image sensor is widely used owing to its low power consumption, a fabrication process simpler than the CCD fabrication process, and the possibility to fabricate as and integrate signal processing circuitry onto one chip.
In expressing a quality of the image sensor, one of the important criteria is dynamic range. In general, the dynamic range is a maximum range in which a signal can be processed without distortion of the signal. The image sensor can obtain a better image regardless of the range of illuminance change if the dynamic range increases.